↵a Pooled antisera raised against rPorB preparations were tested for their ability to induce complement-mediated killing of the homologous strain H44/76 (serotype 15), and against two heterologous strains also expressing PorB3, strains MC139 (serotype 4) and MC167 (serotype 15). Sera were tested in series of dilutions; the titer is the highest dilution of sera which produced >50% killing. −, <50% killing at the lowest dilution tested (1/4); ND, not determined.